Generally in the past, structural parts for vehicles such as aircraft have been made from metals such as, for example, titanium or aluminium or similar alloys, depending upon the function of the part. Increasingly in recent years, composite materials have been used to manufacture certain parts of an aircraft, such as, for example, a wing skin. Similarly, fuselage skins, which have generally been constructed of aluminium and titanium in the past, have begun to be replaced with composite materials.
When incorporating composite materials into structures it is generally necessary to provide a layup in a mould, and such a mould is commonly referred to as the “tooling” for the forming process. The composite materials are then cured under high pressure, in the tooling, to create the necessary component. Manufacturing costs of such tooling and the resulting investment are high, as the tooling is specific to a particular component, has to be much larger and structurally more robust than the component which it is used to manufacture. Traditional tooling therefore has a high non-recurring cost (NRC). Further, any changes in the shape or design of the component being formed can result in at least re-working of the tooling being necessary, or potentially complete disposal of the tooling and re-manufacture of new tooling, resulting in a high re-tooling cost of any design revisions.
An issue which arises with the increasing use of composite materials is how to deal with the relatively large tolerances which are inherent in the curing process and result in low predictability of cured part thickness (CPT) and uncured part thickness (UCPT). This can make the assembly procedure more complex and time consuming, since adjustment and compensation for varying tolerances of composite parts must be made during the assembly procedure. Further, the attachment of neighbouring components to composite parts can be difficult and forming the necessary projections, lugs and attachment portions to enable this can be a complex and expensive procedure. Moreover, due to the non-conductivity of composite parts, compensatory adjustments and additional conductive paths may need to be incorporated in the structure or overall assembly in certain cases, to ensure effective lightning strike protection of the structure as a whole. This is particularly the case in aircraft structures.